Liquid crystal panels can not emit light by themselves, and thus they need to be used with backlight sources. Most products in the market use LED backlights since LED backlights have advantages of, such as, light weight, small thickness and low power dissipation. In a large size liquid crystal panel, there are many LED lamps and the drive currents thereof will be large, and therefore driving voltage differences among a plurality strings of LED lamps will be large. FIG. 1 is a schematic diagram of prior art driving method of an LED lamp. In a traditional LED driving mode, for a positive driving voltage, a driving voltage with the largest voltage drop among the plurality strings of LED lamps is selected as a driving voltage for the entire backlight assembly, and thus for LED lamp strips with small voltage drops, remaining voltage will be completely applied on LED driving chips. At the same time, since LED driving currents for large size panels are generally large, when a voltage difference is applied to an LED driving chip, the chip may be burnt due to large amount of heat.
For the voltage differences among the LED lamp strips, theoretically, the smaller the voltage differences are, the smaller the heat generated by the LED driving chips will be. However, in practice, it is difficult to control the voltage differences between the lamp strips, and at the same time, distinguishing process may cause cost increase.